Not Applicable
Not Applicable
Not Applicable
The present invention relates to pressure sensors, and more particularly, to pressure sensor networks that include temperature compensation mechanisms so as to be relatively insensitive to variations in ambient temperatures.
Prior art pressure sensor networks related to the present invention generally include a transducer component and a driver output component. A block diagram of an exemplary prior art pressure sensor network 10 is shown in FIG. 1. The transducer component 12 includes a capacitive or inductive pressure sensor 14 that produces a varying parameter 16, either capacitance or inductance, as a function of an applied pressure 18. For example, a capacitive transducer may incorporate a flexible, electrically conductive diaphragm positioned parallel to a stationary, electrically conductive plate at a nominal distance d. In this case, the variable parameter 16 includes the capacitance across the diaphragm and the stationary plate. Pressure applied to the flexible diaphragm causes the distance d to change, thus causing the capacitance to change.
The driver component 20 uses this varying parameter 16 as a component of a resonant tank circuit 22, such that the resonant frequency of the tank circuit varies as a function of the applied pressure 18. The driver component 20 produces a pressure signal 24 corresponding to the magnitude of the applied pressure 18. The pressure signal 24 may simply be the raw signal that the resonant tank circuit 22 generates, such that the frequency of the pressure signal 24 conveys the information regarding the applied pressure 18.
Alternately, the driver component 20 may perform a frequency-to-voltage or frequency-to-current conversion on the raw signal from the tank circuit 22, such that the voltage or current, respectively, of the pressure signal 24 conveys the information regarding the applied pressure 18. The pressure sensor network 10 may further include a processor 26 for receiving and converting the pressure signal 24 into a form that is more useful to a particular application. For example, the processor 26 may sample the pressure signal 24 and convert the embedded pressure information into a digit format that is useful to other processing components.
Due to physical characteristics of the pressure sensor 10, the relationship between the applied pressure 18 and the pressure signal 24 may vary as a function of external conditions that produce a change in the physical dimensions of pressure sensor 10. One exemplary external condition that can produce such a change is the ambient temperature, although other external conditions (e.g., humidity) can also produce such changes. For example, in a pressure sensor that incorporates a capacitive transducer as described hereinbefore, temperature variations typically cause dimensional variations to the diaphragm and conductive plate, which in turn modify the relationship between the applied pressure and the pressure signal. This relationship between the sensor temperature and the pressure to output relationship is commonly referred to as the temperature sensitivity of the sensor. Schemes to compensate for such temperature sensitivity typically involve characterizing temperature sensitivity over the operating temperature range, measuring the temperature of the transducer in real time and applying a compensating factor to the pressure signal 24 according to the characterized temperature sensitivity at the measured temperature.
One disadvantage to such compensation schemes is that in order to measure the transducer temperature in real time, additional components such as thermistors, thermocouples, etc., along with associated sensing circuitry, must be added to the pressures sensor. These additional components add cost and complexity to the sensor, and reduce overall reliability.
Another disadvantage to such compensation schemes is that often the transducer portion of the pressure sensor is physically removed from the driver portion, such that their respective temperatures may be different. When the driver portion of the sensor includes components that are also subject to temperature sensitivities, the different temperatures tend to compound the overall temperature sensitivity of the sensor, further complicating the compensation problem.
It is an object of the present invention to substantially overcome the above-identified disadvantages and drawbacks of the prior art.
The foregoing and other objects are achieved by the invention which in one aspect comprises a temperature compensated pressure sensor network for providing an output sensing signal representative of an applied pressure. The sensor network includes a reference oscillator circuit for providing a reference signal having an associated reference frequency. The oscillator circuit includes a first inductor, wherein the reference frequency is a predetermined function of a first inductance associated with the first inductor. The sensor network further includes a sensor circuit for providing a sensing signal having an associated sensing frequency. The sensor circuit includes a second inductor and a sensing capacitor electrically coupled in series, wherein the sensing frequency is a predetermined function of a second inductance associated with the second inductor pair and the applied pressure. The sensor network also includes a processor for receiving the reference signal and the sensing signal, and producing the output sensing signal. The output sensing signal is a predetermined function of the reference signal and the sensing signal. The first inductor pair is oriented with respect to the second inductor pair so as to minimize effects of inductive coupling, and parametric variation, between the first inductor and the second inductor. The parametric variation may include a variation in one or more physical dimensions due to temperature, humidity, and other external conditions or combinations of conditions. In an alternate embodiment, the first inductor includes an inductor pair electrically coupled in series, and the second inductor includes an inductor pair electrically coupled in series.
In another embodiment of the invention, the first inductor and the second inductor are electrically coupled in series opposition, and the third inductor and the fourth inductor are electrically coupled in series opposition.
In another embodiment of the invention, the first inductor pair is oriented substantially orthogonal to the second inductor pair.
In another embodiment of the invention, the first inductor pair including a first planar inductor and a second planar inductor disposed in a plane along a first axis, the second inductor pair including a third planar inductor and a fourth planar inductor disposed in the plane along a second axis.
In another embodiment of the invention, the first axis and the second axis are substantially orthogonal, and the first axis intersects the second axis at a point substantially equidistant between the first planar inductor and the second planar inductor.
In another embodiment of the invention, the first planar inductor produces a first flux in a direction substantially orthogonal to the plane, the second planar inductor produces a second flux in a direction substantially parallel but opposite to that of the first flux, the third planar inductor produces a third flux in a direction substantially orthogonal to the plane, and the fourth planar inductor produces a fourth flux in a direction substantially parallel but opposite of the third flux.
In another embodiment of the invention, a first distance from a center of the first planar inductor to a center of the third planar inductor is substantially equal to a second distance from a center of the second planar inductor to a center of the third planar inductor.
In another embodiment of the invention, a first distance from a center of the first planar inductor to a center of the fourth planar inductor is substantially equal to a second distance from a center of the second planar inductor to a center of the fourth planar inductor.
In another embodiment of the invention, the processor executes a sequential procedure using the reference signal as a sequencing timebase and the sensing signal as an input, such that a variation in the reference frequency compensates for a variation in the sensing frequency.
In another embodiment of the invention, the sensing capacitor is characterized by an associated capacitance that varies as a predetermined function of the applied pressure.
In another aspect, the invention comprises a method of providing an output sensing signal representative of an applied pressure. The method includes the step of providing a reference signal having an associated reference frequency and being generated by an oscillator circuit including a first inductor pair electrically coupled in series. The reference frequency is a predetermined function of a first inductance associated with the first inductor pair. The method further includes the step of providing a sensing signal having an associated sensing frequency and being generated by a sensor circuit including a second inductor pair and a sensing capacitor electrically coupled in series. The sensing frequency is a predetermined function of a second inductance associated with the second inductor pair and the applied pressure. The method also includes the step of producing the output sensing signal being a predetermined function of the reference signal and the sensing signal. The method further includes the step of orienting the first inductor pair with respect to the second inductor pair so as to minimize effects of inductive coupling, and parametric variation, between the first inductor pair and the second inductor pair. The parametric variation may include a variation in one or more physical dimensions due to temperature, humidity, and other external conditions or combinations of conditions.
Another embodiment of the invention further includes the step of orienting the first inductor pair substantially orthogonal to the second inductor pair.